Central features required of sensors of angular velocity are resistance to vibration and impact. Particularly in applications in the automotive industry, for example, such as driving stability control systems, these requirements are extremely tight. Even a violent external blow, e.g. from a stone, or vibration caused by a car stereo, should not interfere with the output of the sensor of angular velocity.
In many micro-mechanical resonators, like e.g. sensors of angular velocity, designing a coupling spring between the moving masses would be preferable, which spring would enable opposite phase motion of the masses and, at the same time, would resist common mode motion of the masses. Such an arrangement is needed particularly for distinguishing various disturbances from the actual signal, such as instances of mechanical impact. Usually, the signal detected from the masses is differential, whereas acceleration influencing them equally causes a common mode displacement.
In FIG. 1, a diagram is shown of a prior art simple coupled resonator, in which the coupling spring J is an identical one-dimensional spring like the other ones. Thus, the simple coupling resonator consists of two masses m1, m2 and three identical one-dimensional springs J. The structure according to FIG. 1 efficiently separates the masses' common mode of motion from the differential mode. However, the structure is unfavorable from the standpoint of acceleration sensitivity, since the masses are more easily displaced in the same phase (the frequency of the mode being lower) than in opposite phase, because the coupling spring will not participate in the motion in the same phase.
In the U.S. patent publication U.S. Pat. No. 6,752,017 B2 particularly depicted are coupled spring structures for a Z-axis gyro, wherein the detection motion is a vibration in opposite phases of masses on a common axis of motion. A common feature of these spring structures is, that they participate in defining both the primary mode and the secondary mode frequencies, and, according to the patent publication, they are positioned between the masses to be coupled, which are located next to each other.
However, the spring structures described in the patent publication have some drawbacks. For example, sensitivity to linear acceleration, because, like the simple coupled resonator described above, they have more slackness for common mode than for opposite phase motion. Thus, blows and vibration displace the masses more easily than does the desired excitation required for the vibration mode in opposite phases. Further, non-linearity in the primary mode is hard to control, because the spring structures participate in both modes. In fact, it would be preferable completely to separate the coupling spring structures for the different modes from each other, such that the non-linearity of the primary mode suspension could be dimensioned independently from the secondary suspension.
A clearly better solution from the viewpoint of mechanical interference, when having vibrating masses with parallel axes, is a seesaw type coupling spring, since it is stiffer for displacement in the same phase than for displacement in opposite phases. Such a coupling suspension is, for example, implemented in the patent application FI 20095201, for which priority is claimed, for primary motion in the y direction of excitation frames, and also presented in FIG. 2, which shows a sensor of angular velocity for the Z axis, in which is shown an example of a seesaw type coupled spring structure in the top and bottom ends in the y axis direction.
However, the angular velocity sensor structure of FIG. 2 completely lacks coupling between the masses inside the frames, whereby, in the x axis direction, the masses operate as nearly independent acceleration sensors. Being uncoupled, they are mechanically almost as sensitive to (common mode) mechanical interference as they are to any opposite phase Coriolis force to be detected. Thus, the question remains open, how preferably to design a coupling suspension for the masses, which would prevent their motion in the same phase, but still would not participate in the primary motion in the y axis direction.
A seesaw suspension similar to the one described above constitutes a working solution with masses moving along, as such, parallel and side by side located axes, but considering a tightly packed structure, takes rather a lot of space. Such a structure provided with masses moving opposite to each other on a common axis, which in a way is even wasteful, is roughly illustrated in FIG. 3. One can clearly see from FIG. 3, that such a structure occupies almost the whole space between the masses, which previously was used for the excitation comb structures of the primary motion.
Thus, the problem remains unsolved, how to implement a structure, at the same time compact and still capable of operating in opposite phase vibrating mode more willingly than in the same phase, and how to then, as a consequence of the opposite phase mode, one could utilize the advantages offered by the opposite phase for e.g. removing interference.
With the technique according to the embodiments of the invention, a solution is obtained to the problem presented above and also to other associated problems; and, if not completely resolved, the effects of the problems will be at least alleviated.
The micro-mechanical resonator according to the invention is characterized in what is mentioned in the characterizing part of the independent claim related to the same.
The sensor according to the invention is characterized in what is mentioned in the characterizing part of the independent claim related to the same.
The vehicle according to the invention is characterized in what is mentioned in the characterizing part of the independent claim related to the same.
The navigator according to the invention is characterized in what is mentioned in the characterizing part of the independent claim related to the same.
The system of micromechanical resonators comprises at least one micromechanical resonator that comprises two masses (M1 M2) that are coupled in direction of their common motion axis with spring structure (401, 402, 403, 404a, 404b, 404c) that comprises at least two beams (402) connected to the masses and spring suspension (404a, 404b, 404c) parallel to the motion axis coupling the beams that deflects perpendicularly to the motion.
In the dependent claims, other preferable embodiments of the invention are presented.